/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.runtime.management;

import org.apache.flink.util.NetUtils;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;
import java.util.Iterator;
import java.util.Optional;

/**
 * Provide a JVM-wide singleton JMX Service.
 */
public class JMXService {
	private static final Logger LOG = LoggerFactory.getLogger(JMXService.class);
	private static JMXServer jmxServer = null;

	/**
	 * Acquire the global singleton JMXServer instance.
	 */
	public static Optional<JMXServer> getInstance() {
		return Optional.ofNullable(jmxServer);
	}

	/**
	 * Start the JMV-wide singleton JMX server.
	 *
	 * <p>If JMXServer static instance is already started, it will not be
	 * started again. Instead a warning will be logged indicating which port
	 * the existing JMXServer static instance is exposing.
	 *
	 * @param portsConfig port configuration of the JMX server.
	 */
	public static synchronized void startInstance(String portsConfig) {
		if (jmxServer == null) {
			if (portsConfig != null) {
				Iterator<Integer> ports = NetUtils.getPortRangeFromString(portsConfig);
				if (ports.hasNext()) {
					jmxServer = startJMXServerWithPortRanges(ports);
				}
				if (jmxServer == null) {
					LOG.error("Could not start JMX server on any configured port(s) in: " + portsConfig);
				}
			}
		} else {
			LOG.warn("JVM-wide JMXServer already started at port: " + jmxServer.getPort());
		}
	}

	/**
	 * Stop the JMX server.
	 */
	public static synchronized void stopInstance() throws IOException {
		if (jmxServer != null) {
			jmxServer.stop();
			jmxServer = null;
		}
	}

	public static synchronized Optional<Integer> getPort() {
		return Optional.ofNullable(jmxServer).map(JMXServer::getPort);
	}

	private static JMXServer startJMXServerWithPortRanges(Iterator<Integer> ports) {
		JMXServer successfullyStartedServer = null;
		while (ports.hasNext() && successfullyStartedServer == null) {
			JMXServer server = new JMXServer();
			int port = ports.next();
			try {
				server.start(port);
				LOG.info("Started JMX server on port " + port + ".");
				successfullyStartedServer = server;
			} catch (IOException ioe) { //assume port conflict
				LOG.debug("Could not start JMX server on port " + port + ".", ioe);
				try {
					server.stop();
				} catch (Exception e) {
					LOG.debug("Could not stop JMX server.", e);
				}
			}
		}
		return successfullyStartedServer;
	}
}
